All neutral atoms contain the same number of protons & electrons. The number of protons determines the element's identity. For instance, 8 protons = oxygen. 17 protons = chlorine. 20 protons = calcium. This does not change.
Electrons determine chemical behavior. Valence electrons (electrons in the outermost energy levels) are significant in this regard, because the number of valence electrons determine how an element behaves in certain conditions. Elements with an octet (8 valence electrons) are unusually stable and do not combine to form compounds (noble gases have an octet, with the exception of helium).
Neutrons determine isotopes. They do not affect the charge or the element's identity. However, they do affect the mass of the nucleus. Several elements have multiple isotopes.